Biocompatible and biodegradable elastomer

ABSTRACT

The present invention provides a biocompatible and biodegradable elastomer, comprising a hard segment and a soft segment. The hard segment is formed by reacting diisocyanate and a chain extender; and the soft segment is comprising a biodegradable oligomer diol, wherein the biodegradable oligomer diol is selected from the group consisting of polycaprolactone diol, polyethylene butylene adipate diol (PEBA diol), poly-L-lactic acid diol (PLLA diol), polylactic acid diol and any combination thereof. The biocompatible and biodegradable elastomer of present invention can be used to produce vascular graft, cell carrier, drug carrier or gene carrier.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Taiwan Patent Application No.102100076 filed on 2 Jan. 2013. All disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a biocompatible and biodegradableelastomer, and, particularly, a biocompatibe and biodegradable elastomersuitable for the use of vascular graft.

2. The Prior Arts

Vascular graft can serve as vascular transplant material and substitutespecific blood vessel in human body that is damaged by aging orpathologies such as atherosclerosis; or serve as graft fistula forpatients undergoing hemodialysis. Vascular transplant materials oftenused in general surgical operations can be biological vascular graft orsynthetic vascular graft.

Biological vascular graft includes autologous transplantation grafts andallogenic transplantation grafts, in which autologous transplantationgrafts are often originated from saphenous veins or internal mammaryarteries. Although saphenous veins and internal mammary arteries areideal material, the source is limited. Allogenic transplantation grafts,on the other hand are usually the chemically treated blood vessels takenfrom animal bodies. Although the source of allogenic transplantationgraft is much abundant, thrombus, vascular tangles, and aneurysm arelikely to occur upon transplanting into human bodies.

The development of synthesized vascular graft dated from the success ofvinyl chloride-acrylonitrile copolymer fiber (Vinyon N) vascular graftintroduced by Voorhees in 1952. It was also been proofed to beclinically applicable. Synthesized vascular graft can also becategorized into non-biodegradable or biodegradable vascular graftaccording to its material. With respect to biological vascular graft,synthesized vascular graft is unlikely to cause problems such as immuneresponse, thrombus, or vascular calcification, thus is considered to bethe more ideal vascular graft for transplantation.

Biomedical materials for the applications of vascular graft preparationshould take into account of factors such as good biocompatibility,outstanding flexibility and compliance, appropriate pore size, andhaving functional endothelial layer. Vascular graft, according to thediameter, can be divided into large diameter (>8 mm) vascular graft,medium diameter (6 to 8 mm) vascular graft, and small diameter (<6 mm)vascular graft (or namely small vascular graft). Small vascular graftswith diameter less than 6 mm can be used to substitute blood vesselswith lower blood flow such as arteriole, coronary artery, or groinartery, however, currently the replacement of arteriole or vein withsmall vascular graft yet to reach satisfactory results due toundesirable long-term patency, as well as problems such as inner layerthickening of angiogensis and vascular narrowing or blocking. Hence, thedevelopment of small vascular grafts that possess similarcharacteristics to human artery and vein as well as goodbiocompatibility to minimize problems of inner layer thickening of thenewborn vessel is a critical task for modern vascular graft engineering.

Biodegradable elastomer is the macromolecule that exhibits advantagessuch as elasticity and biodegradability as well as goodbiocompatibility, mechanical property, and workability, and can bewidely used in the field of biomedicine, for example, hard tissueembedding, repairing material, surgical suture, carrier for drugrelease, and vascular tissue engineering. Thus, the development of abiocompatible and biodegradable elastomer with features that can be usedas vascular graft can dramatically promote the advance of vasculartissue engineering.

SUMMARY OF THE INVENTION

The accomplish the abovementioned industrial needs, the presentinvention provides a biocompatible and biodegradable elastomer,comprising: a main chain of polyurethane comprising a hard segment and asoft segment, the hard segment is formed by reaction of diisocyanate anda chain extender, and the soft segment is a biodegradable oligomer diol,wherein the biodegradable oligomer diol is selected from the groupconsisting of polycaprolactone diol, polyethylene butylene adipate diol,polylactic acid diol, and any combinations thereof.

In one embodiment of the present invention, the amount of the softsegment is between 45% and 75% w/w of the total weight of the elstomer.The polylactic acid diol is L-lactic acid or DL-lactic acid. When thesoft segment is consisted of polycaprolactone diol and polyethylenebutylene adipate diol, the polycaprolactone diol is in an amount ofgreater than 0.3 molar fraction of the degradable oligomer diol; whenthe soft segment is consisted of polycaprolactone diol and polylacticacid diol, the polycaprolactone diol is in an amount of greater than 0.4molar fraction of the degradable oligomer diol; and when the softsegment is consisted of polycaprolactone diol and polylactic acid diol,the polycaprolactone diol is in an amount of greater than 0.8 molarfraction of the degradable oligomer diol. The diisocyanate is alicyclicpolyisocyanate, and preferably, isophorone diisocyanate, whereas thechain extender is preferably ethylenediamine.

Another aspect of the present invention is to provide biocompatible andbiodegradable elastic membrane made of the above biocompatible andbiodegradable elastomer, wherein the Young's modulus of thebiocompatible and biodegradable elastic membrane is greater than 0.5 MPaand smaller than 40 MPa, the tensile strength of the biocompatible andbiodegradable elastic membrane is greater than 5 MPa and less than 50MPa, the elongation of the biodegradable elastic membrane is greaterthan 400%.

Another aspect of the present invention is to provide a vascular graftmade of the above biocompatible and biodegradable elastomer, wherein aplurality of pores are present on the wall of the vascular graft with anaverage pore diameter on the outer surface is between 5 to 50 μm, and anaverage pore diameter on the cross-section is between 10 to 100 μm. Theelongation of the vascular graft is greater than 220%, and the pores aremade by using freeze drying or particle-leaching method; additionally,the surface of the wall of the vascular graft can be chemicallymodified.

Another aspect of the present invention is to provide a carrier made ofthe above biocompatible and biodegradable elastomer, wherein the carrieris present in the form of microsphoere, hydrogel, nanodispersion,nanodispersion-coated inorganic nanoparticle, foam, electrospinningfiber, or scaffold. The carrier exhibits electronegativity,amphiphilicity, and anticoagulant ability and is used for carrying acell, a gene, or a drug.

According to the technical features of the present invention, abiocompatible and biodegradable elastomer can be obtained, and theelastomer can further be made into scaffold which the diameters of thepores on the surface and the cross-section are within the range of thediameter of vascular graft endothelialization. Additionally, thescaffold not posses significant blood coagulation function. Endothelialcells and adipose-derived stem cells can be successfully implanted ontothe scaffold and proliferate. The scaffold also exhibits goodbiocompatibility with no inflammatory response and low allogenicresponse, which indicates being an ideal material for vascular graft.Moreover, the characteristics of electronegativity andnon-blood-platelet-activation of the biocompatible and biodegradableelastomer of the present invention indicating its anticoagulant ability.

On the other hand, the biocompatible and biodegradable elastomer of thepresent invention possesses good dispersion stability and bloodcompatibility. The biocompatible and biodegradable elastomer of thepresent invention from hydrogel by increasing temperature, or preparedin the form of microsphere, fiber, 3D foam, and sophisticated scaffold.This advantages of various waterborne workability allow thebiocompatible and biodegradable elastomer of the present invention to bewidely used in the field of biomedicine.

The present invention is further explained in the following embodimentillustration and examples. Those examples below should not, however, beconsidered to limit the scope of the invention, it is contemplated thatmodifications will readily occur to those skilled in the art, whichmodifications will be within the spirit of the invention and scope ofthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the TEM image of the waterborne biodegradable polyurethaneemulsion.

FIGS. 2(a) and (b) are the entitative image of the waterbornebiodegradable polyurethane emulsion in low and high temperature; (c) isthe Rheology analytical result of the waterborne biodegradablepolyurethane emulsion.

FIG. 3 is the inflammatory test of murine macrophage using differentwaterborne biodegradable polyurethane.

FIG. 4 is the relationship of the remaining percentage of weight of thewaterborne biodegradable polyurethane under the accelerated degradationby PBS at 50° C., wherein (a) indicates soft segment consisting of PCLdiol and PEBA diol; (b) indicates soft segment consisting of PCL dioland PLLA diol; (c) indicates soft segment consisting of PCL diol andPDLLA diol.

FIG. 5 is the relationship of the remaining percentage of weight of thewaterborne biodegradable polyurethane under the accelerated degradationby NaOH at 37° C., wherein (a) indicates soft segment consisting of PCLdiol and PEBA diol; (b) indicates soft segment consisting of PCL dioland PLLA diol; (c) indicates soft segment consisting of PCL diol andPDLLA diol.

FIG. 6 is the remaining percentage of weight and the remainingpercentage of molecular weight before and after implantation. (*p<0.05;**p<0.05)

FIG. 7 is the surface configuration of electrospinning fibers, wherein(a, f) indicate PLA^(e); (b, g) indicate PCL100^(e); (c, h) indicatePCL40EB60^(e); (d, i) indicate PCL80LL20^(e); (e, j) indicatePCL80DL20^(e).

FIG. 8 is the surface configuration of membrane freeze dried at −20° C.,wherein (a, f) indicate PLA^(f); (b, g) indicate PCL100^(f); (c, h)indicate PCL40EB60^(f); (d, i) indicate PCL80LL20^(f); (e, j) indicatePCL80DL20^(f); (a, b, c, d, e) indicate the surface configuration and(f, g, h, i, j) indicate the cross-section configuration.

FIG. 9 is the SEM image of the foams of waterborne biodegradablepolyurethane emulsion formed by 10% dilution and freeze drying, where(a) is the top view and (b) is the bottom view.

FIG. 10 is the surface configuration of scaffold obtained by usingglucose in particle-leaching and freeze drying at −20° C., wherein (a,f) indicate PLA^(s); (b, g) indicate PCL100^(s); (c, h) indicatePCL40EB60^(s); (d, i) indicate PCL80LL20^(s); (e, j) indicatePCL80DL20^(s); (a, b, c, d, e) indicate the surface configuration and(f, g, h, i, j) indicate the cross-section configuration.

FIG. 11 is the analytical results of freeze dried membrane with surfacemodification by sulfonated chitosan using Attenuated Total ReflectionFourier Infrared Spectroscopy.

FIG. 12 is adhesion at 24 hours and proliferation 72 hours ofendothelial cells (ECs) in the cell seeding density of 2×10⁴ cell/wellusing different electrospinning fibers. (*p<0.05; **p<0.05)

FIG. 13 is adhesion at 24 hours and proliferation 72 hours ofendothelial cells (ECs) in the cell seeding density of 2×10⁴ cell/wellusing different freeze dried membrane. (*p<0.05; **p<0.05)

FIG. 14 is adhesion at 24 hours and proliferation 72 hours ofendothelial cells (ECs) in the cell seeding density of 2×10⁴ cell/wellusing freeze dried membrane with surface modification. (*p<0.05)

FIG. 15 is seeding rate of rat adipose-derived stem cells (rADAS) at 24hours using different freeze dried scaffold. (*p<0.05)

FIG. 16 is amount of blood platelet adhesion using different freezedried membrane. (*p<0.05; **p<0.05; ‡p<0.05)

FIG. 17 is the structurally opened 3D scaffold with stacking regularmicropillar made by waterborne biodegradable polyurethane emulsion,wherein (a) is the visible appearance and (b to d) are SEM images withdifferent magnifying powers.

FIG. 18 is the drug carrying ability of PCL40EB60 microsphere and PCL100microsphere.

FIG. 19 is cell carrying ability of PCL100 microsphere.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Definition

As used herein, unless otherwise specified, the term “biocompatible andbiodegradable polyurethane”, “waterborne biodegradable polyurethane”,“biodegradable polyurethane” or “biodegradable elastomer” refers to the“biocompatible and biodegradable elastomer” of the present invention.

As used herein, unless otherwise specified, the term “amphiphilicity”refers to the characteristic of being hydrophilic and hydrophobicsimultaneously.

One embodiment of the present invention is to prepare a biocompatibleand biodegradable elastomer which is waterborne without cross-linkingsystem, comprising a main chain of polyurethane which comprises a hardsegment and a soft segment, the hard segment is formed by reaction ofdissocyanate and a chain extender, and the soft segment is formed byreaction of a biodegradable oligomer diol and polycaprolactone diol (PCLdiol). The biodegradable oligomer diol is polyethylene butylene adipatediol (PEBA diol) or polylactic acid diol. More specifically, thepolylactic acid diol is poly-L-lactic acid diol (PLLA diol) orpoly-DL-lactic acid diol (PDLLA diol).

The amount of the soft segment is between 45% and 75% w/w of the totalweight of the biocompatible and biodegradable elstomer of the presentinvention, and in one embodiment of the present invention, the amount ofthe soft segment is represented by 65% w/w of the total weight of thebiocompatible and biodegradable elastomer.

In another embodiment of the present invention, coating or graftingsulfonated chitosan onto the surface of the biocompatible andbiodegradable elstomer is disclosed, and this material is made intotubular shape such as but not limited to artificial vascular graft, theelstomer can also be made into porous body, membrane, and cell scaffold.

The biocompatible and biodegradable elastomer of the present inventionis used in the murine macrophage inflammatory test to proof that thebiocompatible and biodegradable elastomer of the present invention doesnot activate macrophage and not cause inflammatory response. On theother hand, by the degradation test at 50° C. using PBS, thebiocompatible and biodegradable elastomer of the present invention isproofed to exhibit higher degradation rate comparing to the polyurethaneof the control groups. The biocompatible and biodegradable elastomerhaving different soft segments exhibit different degradation rateaccording to the components and proportions.

In another embodiment of the present invention, the biocompatible andbiodegradable elastomer is made into scaffold by using electrospinning,freeze drying, and particle-leaching method. The diameter of pores onthe surface and cross-section pores of the scaffold made using thesethree methods are within the pore diameter range required for vasculargraft endothelialization, thus, the scaffolds made of the biocompatibleand biodegradable elastomer are ideal material for vascular graft.

The abovementioned scaffold is subjected to biocompatibility test, inthe endothelial cell adhesion and proliferation test, the scaffold madeof the biocompatible and biodegradable elastomer of the presentinvention exhibits significant higher adhesion rate and proliferationrate comparing to the control group (TCPS medium), thus, can promote theadhesion and proliferation of endothelial cells, hence, promote theangiogensis. On the other hand, in the adipose-derived stem cell seedingrate test, the scaffold made of the biocompatible and biodegradable ofthe present invention shows significant higher seeding rate than thecontrol group (PLA), indicating that cells can be successfully implantedonto the scaffold and can survive and proliferate without wet condition.In the blood platelet adhesion test, a tendency to decrease regardingblood platelet adhesion and activation can be observed after the surfacemodification, indicating that surface modification can suppress bloodplatelet adhesion and activation.

In the embodiments of the present invention, the terminology of thewaterborne biodegradable polyurethane in different ratio is shown inTable 1. In addition, the waterborne biodegradable polyurethane madeusing electrospinning, freeze drying, or particle-leaching methodincorporated with freeze drying are represented by using an upper indexof e, f, or s, respectively, as suffixes; different waterbornebiodegradable polyurethane with surface modification of sulfonatedchitosan are represented by using “-ASC” as suffixes.

In embodiments of the present invention, experimental results areexpressed as mean±standard error of the mean. Mean was analyzed usingthe t-test. Statistically significant difference was set at the level ofP<0.05.

EXAMPLE 1 Preparation of Degradable Elstomer

1-1 Formulation

The different soft segments were prepared by mixing three differentdegradable (water degradable) oligomer diols and polycaprolactone diolwith several ratios so as to synthesize various degradable polyurethanein which the rate of degradation is controllable. The three differentsoft segments are shown in Table 1, where EB represents PEBA, LLrepresents PLLA and DL represents PDLLA. The soft segment with 20 wt %polylactic acid diol is shown in Table 2. Firstly, 4.4 wt % of2,2-bis(hydroxymethyl)propionic acid (DMPA, Aldrich) was fixed. Themolar ratio of isocyanate functional group and hydroxyl group of theprepolymer before water-dispersion was set at 1.9 (NCO/OH), while themolar ratio of isocyanate functional group and hydroxyl group plus aminegroup of the prepolymer after water-dispersion was set at 1.08(NCO/(OH+NH₂)). Additionally, 85 mol % of chain extender with solidcontent of 30 wt % was added. The ratio of IPDI:marcodiols:DMPA:EDA:TEAwas 3.76:1:1:1.51:1. The detailed formulation is shown in Table 3.

The waterborne biodegradable polyurethane PCL100 is formulated byreplacing the proportion of soft segment or diol shown in Table 2 andTable 3 with 100% polycaprolactone diol. The PCL40EB60 is formulated byreplacing the proportion of soft segment or diol shown in Table 2 andTable 3 with 40% polycaprolactone diol and 60% polyethylene butyleneadipate diol.

TABLE 1 Different waterborne biodegradable polyurethane with Softsegments Molar ratio of the soft segment PCL PEBA PDLA PLLAPrepolymerization Sample diol diol diol diol temperature (° C.) PCL100100 — — — 75 PCL40EB60 40 60 — — 75 PCL80LL20 — 80 — 20 95 PCL80DL20 —80 20 — 75

TABLE 2 Waterborne biodegradable polyurethane with soft segment of 20 wt% polylactic acid Samples of waterborne biodegradable polyurethane P-20Total weight (g) 358 Total solid weight (g) 107 Iso index beforewater-dispersion (NCO/OH) 1.90 Iso index after water-dispersion((NCO/(OH + NH₂)) 1.08 amine mol % of prepolymerized NCO mol % 85 Solidcontent weight % 30 Solvent content weight % 70 Weight of hard segment %35 Weight of PLA diol of the soft segment % 13 Weight of PCL diol of thesoft segment % 52

TABLE 3 Waterborne biodegradable polyurethane with soft segment of 20 wt% polylactic acid diol Molecular weight (g/mol) Molar ratio Weight (g)IPDI 222.28 3.76 14.64 DMPA 134.13 1.00 2.345 PCL diol 2000 0.80 28.00PLA diol 2000 0.20 7.00 EDA 60.1 1.51 1.60 TEA 101.19 1 1.77 MEK 72.1113.00 H₂O 18.02 110.26 T-9 405.12 0.051-2 Synthetic Process

The synthetic process was done by reacting polycaprolactone diol (PCLdiol, Mw=2000 g/mol, Aldrich) with polyethylene butylene adipate diol(PEBA diol, Mw=2000 g/mol, GRECO), poly-L-lactic acid diol (PLLA diol,Mw=2000 g/mol) and poly-DL-lactic acid diol (PDLLA diol, Mw=2000 g/mol),respectively. The poly-L-lactic acid diol is obtained by thering-opening reaction of L-lactide and 1,4-BDO in the molar ratio of13:1 with the addition of catalyst, T-9, under 150° C. for 10 to 12hours followed by temperature reduction to 0 to 4° C., ethanolpurification, vacuum drying, and grinding. The poly-DL-lactic acid diolis obtained by the ring-opening reaction of DL-lactide and 1,4-BDO inthe molar ratio of 13:1 with the addition of catalyst, T-9, under 150°C. for 10 to 12 hours followed by temperature reduction to 0 to 4° C.and vacuum sublimation in a controlled temperature of 120° C.

The above synthesized compounds were added to four-necked separableflask, adjusted to appropriate prepolymerization temperature, andmechanically homogenized at 180 rpm. After the reactant becoming ahomogenized liquid, tin(II)2-ethylhexanoate (T-9, Alfa Aesar) andisophorone diisocyanate (IPDI, Evonik Degussa GmbH) were added ascatalysts. The reactant was then stirred at 180 rpm. The reaction wasproceeded at the prepolymerization temperature for 3 hours.

Then, the temperature is reduced to 75° C. and2,2-bis(hydroxymethyl)propionic acid (DMPA, Aldrich) and methyl ethylketone (MEK, J.T. Backer) were added to the flask. The temperature wasmaintained at 75° C. and the reaction was proceeded at 180 rpm for onehour. Then, the temperature was reduced to 50° C. and trethylamine (TEA,RDH) was added to neutralize the reaction for half an hour. After thereaction was completed, double distilled water was added immediatelyupon reducing the temperature to 45° C. and increasing the rotationspeed to 1100 rpm. After water-dispersion, 50 mol % ethylenediamine(EDA, Tedia) were added twice with a 15 minutes gap in between eachaddition. As a result, waterborne biodegradable polyurethane wasproduced in the form of emulsion. The ratio ofIPDI:marcodiols:DMPA:EDA:TEA of the product was 3.52:1:1:1.52:1. Thesynthetic steps are shown in Scheme 1. The soft segments with differentprepolymerized temperatures (the rightmost column) are shown in Table 1.

The TEM image of the waterborne biodegradable polyurethane emulsion isshown in FIG. 1. The waterborne biodegradable polyurethane emulsion wasanalyzed its particle diameter and surface potential. The resultsindicated that the particle diameter is 39±9 nm and the Zeta Potentialis −58±2 mV. The emulsion is also amphiphilic (hydrophilic andhydrophobic) and negatively charged indicating its anticoagulantability. The emulsion can also be used to stabilize inorganicnanoparticles such as silver nanoparticles and applied to cell uptake orcell tracking.

Besides, waterborne biodegradable polyurethane emulsion PCL80DL20 canform hydrogel at temperatures higher than 37° C. The entitative image ofthe waterborne biodegradable polyurethane emulsion in low and hightemperature are shown in FIG. 2(a) and FIG. 2(b) and the Rheologyanalytical result of the waterborne biodegradable polyurethane emulsionis shown in FIG. 2(c). It is shown from the result that the waterbornebiodegradable polyurethane emulsion forms hydrogel at approximately 37°C. since G′>G″. This characteristic indicates that the waterbornebiodegradable polyurethane can be used as drug carrier or gene carrier.

1-3 Membrane Preparation

The 30 wt % waterborne biodegradable polyurethane emulsion was coatedonto a glass plate using Spiner at 2300 rpm in 20 seconds. Anotherappropriate amount of 30 wt % emulsion was placed on Teflon plate andthen dried for 72 hours at room temperature (25° C.) and vacuumized for48 hours at 25° C. in an oven.

Commercial polyurethane (Pellethane 2363-80A, Pellethane, Upjohn) andpolylactic acid (PLA, NatureWorks 2002D) were used as control groups inthe present embodiment. Pellethane was dissolved in N,N-dimethylacetamide (DMAc, Tedia) to form a 5 wt % solution. An appropriate amountof the Pellethane solution was place on glass plate, and the glass platewas dried in an oven at 60° C. for 72 hours then vacuumized at 60° C.for 48 hours. Polylactic acid was dissolved in 1,4-dioxane (Tedia) toform a 10 wt % solution. An appropriate amount of the polylactic acidsolution was place on Teflon plate and the plate was dried in an oven at60° C. for 72 hours then vacuumized at 60° C. for 48 hours. Thus, themembrane was produced.

According to the procedure above, soft segment of PCL diol mixed withdifferent proportions of PEBA, soft segment of PCL diol mixed withdifferent proportions of PLLA diol, and soft segment of PCL diol mixedwith PDLLA diol can be successfully synthesized into waterbornebiodegradable polyurethane and can be prepared in the form of membranewithout cracking.

EXAMPLE 2 Biocompatibility Analysis of the Biodegradable Polyurethane

2-1 Inflammation Test of Macrophage

Murine macrophages (J774A.1) from 30 to 40 generations were used in thepresent embodiment. Oil-based polyurethane (Pellethane, control group)and the waterborne biodegradable polyurethane subjected to subjected tomembrane formation and vacuumization were firstly sterilized using 75%ethanol, immersed in phosphate buffered saline (PBS) three times toreplace the ethanol, and then place in 24-well corning. The medium usedwas high glucose Dulbecco's modified Eagle's cell medium (Gibco)containing 10% FBS, 1% PSA, and 1.5 g/L Na₂CO₃. Cells were incubated atthe density of 2×10⁴ cell/well at the condition of 37° C. and 5% CO₂ for24 hours and 72 hours. Cell morphology was observed using microscope andcell diameter was analyzed using Multisizer™ 3 COULTER COUNTER®(Multisizer 3, Beckman Coulter, USA).

As shown in Table 4, the inflammatory response of the waterbornebiodegradable polyurethane was tested using murine macrophage. Thewaterborne biodegradable polyurethane was made in contact with the cellsfor 24 hours, and the size difference of cells between the waterbornebiodegradable polyurethane and TCPS was above 0.4 μm, while the sizedifference of cells between the waterborne biodegradable polyurethaneand the control group, Pellethane, was above 0.5 μm. When the waterbornebiodegradable polyurethane was made in contact with the cells for 72hours, the size difference of the cells between the waterbornebiodegradable polyurethane and TCPS remained to be above 0.4 μm, whereasthe size difference of the cells between the waterborne biodegradablepolyurethane and the control group increased to be above 0.6 μm. Thus,the biodegradable polyurethane membrane is proofed not to activatemurine macrophage and result in inflammatory response.

TABLE 4 Cell sizes of murine macrophage cultured using differentmaterials Average cell size (μm) Membrane type 24 hours 72 hours TCPS15.30 ± 0.40 15.53 ± 0.36 Pellethane 15.42 ± 0.25 15.76 ± 0.55 PCL10014.90 ± 0.43 15.13 ± 0.61 PCL40EB60 14.71 ± 0.37 15.01 ± 0.46 PCL80LL2014.64 ± 0.33 14.89 ± 0.54 PCL80DL20 14.64 ± 0.48 14.95 ± 0.492-1-1 Gene Expression of the Murine Macrophage Inflammatory-Related Gene

Cell pellet for analysis was washed twice by PBS. 1 mL of trizol(Invitrogen, USA) was added to dissolve the cells and 200 μL ofchloroform (Tedia) were added to extract RNA. 500 μL of isopropanol (IT.Backer) were then added to the RNA solution extracted to precipitateRNA. The RNA were collected by centrifugation at 12000 rpm for 15minutes and washed by 75% EtOH/DEPC solution to replace isopropanol.Finally, RNase-free DEPC-treated water was used to dissolve RNA. Theabove steps were carried out at 0 to 4° C. and the RNA solution wasstored at −20° C. The RNA samples were quantitatively diluted usingRNase-free DEPC-treated water and the concentration of RNA wasdetermined by the absorbance of 260 nm and 280 nm measured using visiblelight/ultra violet light spectrometer (U-2000, Hitachi).

Reverse transcription was performed by using RevertAid™ First StrandcDNA Synthesis kit (Fermentas, USA). 0.1 to 0.5 μg of RNA were usedaccording to the quantitative result, and 1 μL of oligo dT were added.RNase-free DEPC-treated water was then added to make the volume up to atotal of 12 μL. After reacting at 70° C. for 5 minutes, 4 μL of 5×reaction buffer solution, 1 μL of RiboLock Ribonuclease inhibitor, and 2μL of 10 mM dNTP were added. After reaction at 37° C. for 5 minutes, 1μL of RTase were added. Then, reaction was carried out at 42° C. for 60minutes, and furthermore, at 70° C. for 10 minutes to produce cDNA.

2 μL of 5×PCR Maister, 1 μL of template DNA 1, 1 μL of forward primer, 1μL of reverse primer, and 17 μL of sterilized deionized water wereloaded in 0.2 mL microtube. Thermal cycle (GeneAmp® PCR system 2700, AB,USA) was used. Gene primers were designed as follow: murine IL-1(forward): CCCAAGCAATACCCAAAGAAGAAG (SEQ ID NO: 1); murine IL-1(reverse): TGTCCTGACCACTGTTGTTTCC (SEQ ID NO: 2); murine IL-6 (forward):TTCCATCCAGTTGCCTTCTTG (SEQ ID NO: 3); murine IL-6 (reverse):TCATTTCCACGATTTCCCAGAG (SEQ ID NO:4); murine TNF-α (forward):CGAGTGACAAGCCTGTAGCC (SEQ ID NO: 5); murine TNF-α-32-(reverse):TTGAAGAGAACCTGGGAGTAGAC (SEQ ID NO: 6); murine β-actin (forward):TCCTGTGGCATCCACGAAACT (SEQ ID NO: 7); murine β-actin (reverse):GGAGCAATGATCCTGATCTTC (SEQ ID NO: 8); bovine eNOS (forward):TAGAATTCCCAGCACCTTTGGGAATGGCGAT (SEQ ID NO: 9); bovine eNOS (reverse):ATAGAATTGGATTCACTTCTGTGTTGCTGGACTCCTT (SEQ ID NO: 10); bovine β-actin(forward): AAAGACAGCTATGTGGGAGA (SEQ ID NO: 11); bovine β-actin(reverse): ATGATCTGGGTCATCTTCT (SEQ ID NO: 12). The annealingtemperature was set at 55° C. and automated capillary nucleic acidanalyzer (eGene, HAD-GT12TM) was used to access the measurement of geneexpression.

Capillary electrophoresis was carried out according to the abovereverse-transcription polymerase chain reaction to isolate the four setsof genes of β-actin, IL-1 (interlukin-1), IL-6 (interlukin-6), andTNF-α. Data measured were divided by half the quantitative geneexpression of normal distribution in the cells to give the immunoassayresults.

FIG. 3 indicates the influence of different materials to murinemacrophage inflammatory-related gene expression. At 24 hours, comparingwith TCPS and Pellethane, the waterborne biodegradable polyurethaneexhibits no significant difference regarding Interleukin-1 (IL-1),Interleukin-6 (IL-6), and Tumor necrosis factor-alpha (TNF-α). At 72hours, although slight increases are observed with waterbornebiodegradable polyurethane treated IL-1, IL-6, and TNF-α, the differenceis still not significant comparing with TCPS. Hence, the waterbornebiodegradable polyurethane of the present invention is proof not totrigger significant inflammatory response.

2-2 In Vitro Degradability Test

The waterborne biodegradable polyurethane subjected to membraneformation and vacuumization was cut into square (5 mm×5 mm) according tothe regulation of ISO 10993-13 and immersed in pH 7.4 phosphate bufferedsaline (PBS). The value of solution value over surface area was adjustedto within the range of 1 to 6 cc/mm² and the solution was placed in ovenwith constant temperature of 50° C. After 7, 14, 21, and 28 days, thewaterborne biodegradable polyurethane was collected and the surface waswashed using double-distilled water. The washed waterborne biodegradablepolyurethane was then placed in oven to dry for 24 hours at 50° C.following vacuumization for another 24 hours. The weights of thewaterborne biodegradable polyurethane before and after the experimentwere measured and the remaining percentage by weight was calculatedaccording to Formula 1.

The waterborne biodegradable polyurethane subjected to membraneformation and vacuumization was cut into square (1 cm×1 cm) and immersedin 3 wt % sodium hydroxide (NaOH) and placed in oven with a constanttemperature of 37° C. After 4, 8, 12, and 24 hours, the waterbornebiodegradable polyurethane was collected and the surface was washedusing double-distilled water. The washed waterborne biodegradablepolyurethane was then placed in oven to dry for 24 hours at 37° C.following vacuumization for another 24 hours. The weights of thewaterborne biodegradable polyurethane before and after the experimentwere measured and the remaining percentage by weight was calculatedaccording to Formula 1.Remaining percentage by weight (%)=Wt/Wo×100%  Formula 1Wo is the starting weight (g); Wt is the washed and dried weight afterdegradation

On the other hand, polycaprolactone diol and polyethylene butyleneadipate diol in the ratio of 60:40 and 80:20, as well aspolycaprolactone diol and poly-L-lactide diol in the ratio of 40:60 and60:40 were made into waterborne biodegradable polyurethane respectivelyaccording to the same method disclosed above for comparison.

The accelerated degradation test of the waterborne biodegradablepolyurethane with PBS at 50° C. is shown in FIG. 4. The higher theproportion of PEBA diol, the faster the degradation rate of thewaterborne biodegradable polyurethane when the soft segment was made ofPCL diol and PEBA diol, which results in a remaining weight percentagebetween 84 to 45 wt % after 28 days. The higher the proportion of PLLAdiol, the faster the degradation rate of the waterborne biodegradablepolyurethane when the soft segment was made of PCL diol and PLLA diol,which results in a remaining weight percentage between 84 to 55 wt %after 28 days. The higher the proportion of PDLLA diol, the faster thedegradation rate of the waterborne biodegradable polyurethane when thesoft segment was made of PCL diol and PDLLA diol, which results in aremaining weight percentage between 84 to 71 wt % after 28 days. Inaddition, the accelerated degradation test of the waterbornebiodegradable polyurethane with 3 wt % NaOH is shown in FIG. 5. Thehigher the proportion of PEBA diol, the faster the degradation rate ofthe waterborne biodegradable polyurethane when the soft segment was madeof PCL diol and PEBA diol, which results in a remaining weightpercentage between 83 to 57 wt % after 24 hours. The higher theproportion of PLLA diol, the faster the degradation rate of thewaterborne biodegradable polyurethane when the soft segment was made ofPCL diol and PLLA diol, which results in a remaining weight percentagebetween 83 to 26 wt % after 24 hours. The higher the proportion of PDLLAdiol, the faster the degradation rate of the waterborne biodegradablepolyurethane when the soft segment was made of PCL diol and PDLLA diol,which results in a remaining weight percentage between 83 to 44 wt %after 24 hours.

The in vitro degradation rates of soft segments made of PCL diol andPEBA diol in PBS and NaOH are rated as follow:PCL40EB60>PCL60EB40>PCL80EB20>PCL100. The in vitro degradation rates ofsoft segments made of PCL diol and PLLA diol in PBS and NaOH are ratedas follow: PCL40LL60>PCL60LL40>PCL80LL20>PCL100. The in vitrodegradation rates of soft segments made of PCL diol and PDLLA diol inPBS and NaOH are rated as follow: PCL80DL20>PCL60LL40>PCL80LL20>PCL100.

2-3 Degradability Test of Murine Subcutaneous Implantation

The waterborne biodegradable polyurethane subjected to membraneformation and vacuumization was cut into square (10 mm×10 mm×0.2 mm),sterilized by 75% ethanol, and then immersed in PBS three times toreplace the ethanol. After gas anesthesia, 10 mm×10 mm subcutaneousincisions were done on both side of the spine of adult Sprague-Dawley(SD) rat and the waterborne biodegradable polyurethane membrane of thepresent invention was implanted. After carbon dioxide euthanasia after29 days, the implanted waterborne biodegradable polyurethane membranewas collected, washed by double-distilled water, and vacuumed for 24hours. The weights of the waterborne biodegradable polyurethane membranebefore and after implantation were measured and the remaining percentageof weight was calculated according to Formula 1. The molecular weightsof the waterborne biodegradable polyurethane membrane before and afterimplantation were measured using gel permeation chromatography (GPC,Waters apparatus) and the remaining percentage of molecular weight wascalculated according to Formula 2. In addition, Scanning ElectronMicroscope (SEM, Hitachi S-4800) was used to observe the surface changesof the waterborne biodegradable polyurethane membrane before and afterimplantation.Remaining percentage of molecular weight (%)=Mt/Mo×100%  Formula 2Mo is the starting molecular weight (Mw); Mt is the washed and driedmolecular weight after degradation

After 29 days of murine subcutaneous implantation, small pores can beseen on the surface of the waterborne biodegradable polyurethane and thediameter of the pores seen on the PLA surface is approximately 5 μm.PCL80DL20 generates more pores during in vivo degradation. Please referto FIG. 6 for the remaining percentage of weight and the remainingpercentage of molecular weight before and after implantation. The leastremaining percentage of weight measured are PLA (55.25%) and PCL80DL20(56.03%) indicating the fastest degradation, whereas the higherremaining percentage of weight measured is PCL 100 (85.66%) indicating aslower degradation. Regarding the remaining percentage of molecularweight before and after implantation, the remaining percentage ofmolecular weight of PLA (19.84%) is the least, the remaining percentageof molecular weight of PCL80DL20 (22.13%) is slight higher, and theremaining percentage of molecular weight of PCL100 (65.27%) is thehighest, indicating the slowest degradation rate. The in vivodegradation rate is rated as follows:PLA PCL80DL20>PCL40EB60 PCL80LL20>PCL100.

EXAMPLE 3 Preparation of scaffold

3-1 Scaffold Preparation by Electrospinning

An electrospinning device was constructed by using high voltage powersupplier (YSTC), syringe pump (KDS-100, KD Scientific, USC), andspinneret (20G, TERUMO). The waterborne biodegradable polyurethanesubjected to membrane formation was dissolved in acetone (Tedia) toprepare 10 to 25 wt % solution and loaded into the syringe pump. Thehigh voltage power supplier was attached with one end to the spinneretand the other to the collector. The flow speed of the syringe and thevoltage were set at 10 to 17 μL/min and 7 to 9 kV, respectively. A layerof aluminum foil or glass plate could be placed on the collector toallow the operating distance between the tip of the spinneret and thecollector to be 19 cm. The electrospinning nano/micro fiber could thenbe collected on the aluminum foil or glass plate and followed byvacuumization at 25° C. for 48 hours. On the other hand,poly(D,L-lactide) (molecular weight=121140 Da, low crystalline, Ingeo2002D, NatureWorks) was dissolved in cosolvent, acetone (Tedia) and1,4-dioxane (Tedia) and loaded into the syringe. For collectingelectrospinning fiber, the flow speed, voltage, and operating distancebetween the tip of the spinneret and the collector were set at 10μL/min, 9 kV, and 19 cm, respectively. Detailed parameters of theelectrospinning fiber are shown in Table 5.

TABLE 5 Parameters of the electrospinning fiber Electrospinning fiberparameters Biodegrad- Operat- able poly- Ace- 1,4- Volt- Flow ingurethane tone dioxane age speed distance Sample (wt %) (wt %) (wt %)(kV) (μl/min) (cm) PCL100 10 90 — 7.1 15 19 PCL40EB60 18 82 — 7.1 10 19PCL80LL20 10 90 — 7.1 15 19 PCL80DL20 25 75 — 7.1 17 19 PLA 10 36 54 9.010 19

The electrospinning fiber obtained by macromolecular solution containingwaterborne biodegradable polyurethane, acetone and polylactic acid,acetone, and 1,4-dioxane under conditions of 10 to 17 μL/min in flowspeed and 7 to 9 kV in voltage is shown in FIG. 7 in which theelectrospinning fiber is thin and fibrous without any occurrence ofbeads. The diameter of PCL100^(e)/acetone (10/90 wt %) is 1.57±0.35 μm;the diameter of PCL40EB60^(e)/acetone (18/82 wt %) is 1.40±0.38 μm; thediameter of PCL80LL20^(e)/acetone (10/90 wt %) is 1.70±0.36 μm; thediameter of PCL80DL20^(e)/acetone (25/75 wt %) is 1.42±0.21 μm; thediameter of PLA^(e)/acetone/1,4-dixane (10/36/54 wt %) is 1.24±0.66 μm.

Moreover, nano fiber with 457.5±44.7 μm in diameter can be fabricated byincorporating polyethylene oxide (PEO) into waterborne biodegradablepolyurethane emulsion and undergoing electrospinning directly.

3-2 Scaffold Preparation by Freeze Drying

3-2-1 Preparation by Freeze Drying

10 mL of 30 wt % waterborne biodegradable polyurethane emulsion wasplaced onto Teflon plate and froze at −20° C. for 24 hours. Then amembrane with thickness of 2 to 3 mm was obtained after freeze dryingusing freeze dryer (FDU-1200, Eyela, Japan) for 24 hours.

The structures of the surface and cross-section of the membrane formedare shown in FIG. 8. For PCL100^(f) freeze dried membrane, the diameterof the pore on the surface is 8.04±2.24 μm and the diameter of the poreon the cross-section is 52.05±19.28 μm; for PCL40EB60^(f) freeze driedmembrane, the diameter of the pore on the surface is 12.74±4.06 μM andthe diameter of the pore on the cross-section is 38.51±16.63 μm; forPCL80LL20^(f) freeze dried membrane, the diameter of the pore on thesurface is 8.86±3.99 μM and the diameter of the pore on thecross-section is 48.61±20.33 μm; for PCL80DL20^(f) freeze driedmembrane, the diameter of the pore on the surface is 25.91±9.04 μM andthe diameter of the pore on the cross-section is 53.70±25.25 μm; forPLA^(f) freeze dried membrane, the diameter of the pore on the surfaceis 49.45±9.04 μM and the diameter of the pore on the cross-section is65.48±10.42 μm. It is shown that the diameters of the pores on thesurface and the cross-section are mostly within the range of thediameter of vascular graft endothelialization.

In addition, foams (as shown in FIG. 9) are formed by diluting thewaterborne biodegradable polyurethane emulsion followed by freeze dryingprocedure. The pores of the foam are larger and more abundant and aredistributed in an asymmetrical manner. The mechanical strength isregardless of dilution, however, with diluted waterborne biodegradablepolyurethane emulsion, the flexibility is better.

3-2-2 Preparation by Particle-Leaching Method and Freeze Drying

Additionally, particle-leaching method was applied. Waterbornebiodegradable polyurethane and PLA (Mw=121.4 kDa, low crystalline, Ingeo2002D, NatureWorks) subjected to membrane formation were separatelydissolved using solvent, 1,4-dioxane (Tedia) to form homogenousmacromolecular solution of PLA/1,4-dioxane (5/95 wt %). Firstly, glucosesource was vacuumized for 12 hours at 60° C. using a vacuum oven in asealed heating environment. Then further vacuumized at 22 to 25° C. for12 hours. Two sieves (ASTM E 11-79 No. 50 and 140) were used to selectglucose particle of 100 to 300 μM in diameter to serve as porogen undercondition of below 20% RH. 2 mL of the solution were placed into acylinder container (diameter=20 mm; thickness=10 mm) having 2 g of sugarparticle (D(+)-glucose anhydrous, Showa, particle diameter=100 to 300μm) for 30 minutes, then froze at −20° C. for 24 hours. After furtherfreeze dried for 24 hours using freeze dryer (FDU-1200, Eyela, Japan),samples (diameter=20 mm; thickness=5 mm) were taken from the cylindercontainer and immersed in water for 24 hours. The water was renewedevery 30 minutes during the process. After the sugar particle and theremaining solvent were fully dissolved in water, samples were taken fromthe water and then freeze dried again for 24 hours using freeze dryer toyield samples of 3 to 4 mm in thickness. Samples were further cut intocylinder with a diameter of 15 mm using casting knife (diameter=15 mm).

The structures of the surface and cross-section are shown in FIG. 10.For PCL100^(s) freeze dried scaffold, the diameter of the pore on thesurface is 160.25±7.49 μM and the diameter of the pore on thecross-section is 139.08±14.75 μm; for PCL40EB60^(s) freeze driedscaffold, the diameter of the pore on the surface is 171.79±20.92 μM andthe diameter of the pore on the cross-section is 186.68±29.27 μm; forPCL80LL20^(s) freeze dried scaffold, the diameter of the pore on thesurface is 207.06±18.04 μM and the diameter of the pore on thecross-section is 152.82±20.46 μm; for PCL80DL20^(s) freeze driedscaffold, the diameter of the pore on the surface is 162.68±4.17 μM andthe diameter of the pore on the cross-section is 149.60±11.71 μm; forPLA^(s) freeze dried scaffold as the control group, the diameter of thepore on the surface is 147.25±13.79 μM and the diameter of the pore onthe cross-section is 147.22±10.23 μm. It is shown that the diameters ofthe pores on the surface and the cross-section are also mostly withinthe range of the diameter of vascular graft endothelialization.

3-3 Mechanical Properties of the Membrane

Different waterborne biodegradable polyurethane membranes subjected tomembrane formation were cut into dumb-bell shape using standard mold(length=20 mm; width=1 mm) For measuring the thickness of the samples,firstly, both edges of the samples were clamped tightly using fixingclamps, then tensile test was carried out at a constant elongation speedset at 100 mm/min using universal tension machine (HT-8504, HungTa).According to stress-strain diagram, the Young's modulus, tensilestrength, and elongation could be determined to compare the physicalstrength of each material.

The Young's modulus of the waterborne biodegradable polyurethane isbetween 0.5 to 40 MPa, while the tensile strength of the waterbornebiodegradable polyurethane is between 5 to 50 MPa. The tensile strengthof the pore-less membrane is greater than 400%, while the tensilestrength of the porous membrane is greater than 220%. Preferred data ofwaterborne biodegradable polyurethane are shown in Table 6.

TABLE 6 Young's 100% Tensile modulus Modulus strength Elongation Sample(MPa) (MPa) (MPa) (%) PCL100 30.9 ± 7.9  5.3 ± 0.1 34.9 ± 3.1  535.5 ±19.7 PCL40EB60 29.9 ± 1.9  4.6 ± 0.3 25.7 ± 5.3  517.2 ± 10.8 PCL80LL2023.2 ± 1.6  6.2 ± 0.3 28.0 ± 3.4  581.1 ± 4.2 PCL80DL20 4.6 ± 0.7 3.8 ±0.2 12.6 ± 3.9  655.5 ± 17.5 PCL100^(f) 5.6 ± 0.9 1.6 ± 0.4 2.2 ± 0.8222.0 ± 25.6 PCL40EB60^(f) 5.0 ± 0.7 1.4 ± 0.2 2.9 ± 0.2 279.0 ± 14.8PCL80LL20^(f) 8.6 ± 0.4 2.4 ± 0.3 3.8 ± 0.3 279.8 ± 5.8 PCL80DL20^(f)1.5 ± 0.4 1.6 ± 0.4 2.5 ± 0.5 287.8 ± 26.4

The waterborne biodegradable polyurethane with soft segment made of PCLdiol and PEBA diol, represented as PCL60EB40, exhibits Young's modulusbetween 24.3 to 33.4 MPa, tensile strength between 25.7 to 34.9, andelongation between 512.7 to 537.4%. The Young's modulus and tensilestrength decreases with the increase of PEBA diol proportion, while theelongation shows no significant changes.

The waterborne biodegradable polyurethane with soft segment made of PCldiol and PLLA diol exhibits Young's modulus between 23.20 to 131.50 MPa,tensile strength between 11.0 to 34.9 MPa, and elongation between 190.0to 581.1%. With the increase of PLLA diol proportion under aprepolymerization temperature of 95° C., Young's modulus shows atendency to decrease and then increase, while tensile strength decreasessignificantly. Elongation, on the other hand, shows a tendency toincrease and then decrease.

The waterborne biodegradable polyurethane with soft segment made of PCLdiol and PDLLA diol exhibits Young's modulus between 4.6 to 31.0 MPa,tensile strength between 12.6 to 34.9 MPa, and elongation between 535.5to 655.5%. With the increase of PDLLA diol proportion, Young's modulusand tensile strength decrease significantly, whereas elongation shows asignificant increase. Overall, PCL100, PCL40EB60, PCL80LL20, andPCl80DL20 are the preferred elastomer having mechanical properties.

As shown in Table 6, freeze dried membrane exhibits Young's modulusbetween 1.5 to 8.6 MPa, tensile strength between 2.2 to 3.8 MPa, andelongation between 220.0 and 287.8%. Scaffold prepared by directlyfreeze drying the waterborne biodegradable polyurethane exhibits a greatmargin of decrease regarding all Young's modulus, tensile strength, andelongation comparing to membrane dried in room temperature.

3-4 Scaffold Surface Modification

The freeze dried waterborne biodegradable polyurethane membrane and apolylactic acid membrane were used. Sulfonated chitosan (Mw=140 kDA,deacetylation degree=95%, sulfonation degree=99%) was grafted usingatmospheric-pressure plasma (San Fang Machinery Co., Ltd., Model Type:FH3001+HTR1001+RD1004) with air mixture of 20% oxygen and 80% nitrogenand inlet pressure of 2.5 kg/cm². The height of nozzle and the speed ofplatform movement were set at 20 mm and 15 m/min, respectively. Afterscanning by atmospheric-pressure plasma, biological solution of chitosanderivatives (2 wt %) were quickly coated onto the membrane to allowreaction to take place for 30 minutes, then the membrane was washed bydouble-distilled water and dried. The surface characteristics aftergrafting were analyzed by contact angle (FTA-1000B, First Ten AngstromCompany, USA), Attenuated Total Reflection Fourier Infrared Spectroscopy(spectrum 100 model, Perkin Elmer), and Scanning Electronic Microscopy(JEOL-JSM-7600).

As shown in FIG. 11, the peak absorption of the freeze dried waterbornebiodegradable polyurethane membrane is 1550 cm⁻¹ for NH₂, 1470 cm⁻¹ forCH₂, 1240 cm⁻¹ for S═O (sulfonic acid), 1160 cm⁻¹ for S═O (sulfone),1040 cm⁻¹ for S═O (sulfoxide), and 780 cm⁻¹ for C—O—S, whereas the peakabsorption of the freeze dried polylactic acid membrane is 1040 cm⁻¹ forS═O (sulfoxide) with a significant increase in absorption peakintensity. On the other hand, regarding the contact angle, PCL100 withsurface modified by sulfonated chitosan decreases to 53.7±1.5°,PCL40EB60 with surface modified by sulfonated chitosan decreases to54.4±3.5°, PCL80LL20 with surface modified by sulfonated chitosandecreases to 57.2±2.5°, PCL80DL20 with surface modified by sulfonatedchitosan increases to 52.1±2.1°, and PLA with surface modified bysulfonated chitosan decreases significantly to 48.3±3.6°. Hence, it isproofed that sulfonated chitosan can be successfully grafted on to thesurface of the freeze dried waterborne polyurethane membrane of thepresent invention.

EXAMPLE 4 Biocompatibility Test of the Scaffold

4-1 Adhesion and Proliferation of Endothelial Cells

Bovine carotid artery endothelial cells (BEC) from 9 to 15 generationswere used. All waterborne biodegradable polyurethane electrospinningfiber (diameter=15 mm), freeze dried membrane (diameter=15 mm), andsurface modified membrane (diameter=15 mm) were firstly sterilized using75% ethanol and immersed in phosphate buffered saline (PBS) three timesto replace the ethanol, then were placed in 24-well corning with anaddition of silicon 0-shaped ring (inner diameter=13 mm), thickness=1mm) located above. LG-DMEM cell culture medium was used and cells wereincubated at the density of 2×10⁴ cell/well at the condition of 37° C.and 5% CO₂ for 24 hours and 72 hours. Cell morphology was observed usingmicroscope, while the adhesion rate at 24 hours and the proliferationrate at 72 hours were calculated using DNA analog.

The cell calibration was plotted. The cell solution was set to 5 to 7concentration gradients and 1 mL of each concentration was freeze driedfor 12 hours and then dissolved in 1.5 mL of decomposition solution (55mM sodium citrate, 150 mM sodium chloride, 5 mM cysteine HCL, 5 mM EDTA,1 mg/21 mL papain) at 60° C. for 24 hours. After dissolving, 0.5 mL ofthe solution were taken and added to 5 mL of dye (10 mM Tris, 1 mMNa2DETA, 0.1 mM sodium chloride, 0.1 g/mL Hoechst). Fluorophotometer wasused to detect the fluorescence intensity (Excitation wavelength=365 nm,Emission wavelength=458 nm). Standard curve of cell quantity was plottedby fluorescence intensity against cell concentration, and the amount ofcells was calculated according to this standard curve.

FIG. 12 represents the results of cell adhesion and proliferation ofendothelial cells using different electrospinning fibers. No significantdifference regarding cell adhesion can be seen at 24 hours, however,after 72 hours, the growth and elongation of the endothelial cells alongthe waterborne biodegradable polyurethane electrospinning fiber can beobserved. PCL80DL20^(e) results in the highest proliferation rate.

FIG. 13 represents the results of cell adhesion and proliferation ofendothelial cells using different freeze dried membrane. At 24 hours,the cell adhesion rate of the freeze dried waterborne biodegradablepolyurethane membrane are all significantly higher than the celladhesion rate of PLA^(f), however, shows no significant differencecomparing to TCPS. The cell proliferation rate of biodegradablepolyurethane is still higher than the cell proliferation rate ofPLA^(f), PCL100f and PCL80LL20^(f), in particular, are higher than TCPS.

FIG. 14 represents the result of cell adhesion and proliferation ofendothelial cells using different surface modified and freeze driedmembrane. At both 24 hours and 72 hours, the cell adhesion rate andproliferation rates of the surface modified and freeze dried membraneshow no significant difference comparing to PLA^(f)-ASC. Theproliferation rate of PCL80LLD20^(f)-ASC is the highest.

4-2 Seeding Rate of Adipose-Derived Stem Cell

Rat adipose-derived adult stem cells from 3 to 5 generations were used.The freeze dried waterborne biodegradable polyurethane scaffold wassterilized using ultraviolet light for an hour and placed into 24-wellcorning. Low glucose DMEM/F12 (low glucose Dulbecco's modified Eagle'smedium/nutrient mixture F-12, DEME-LG/F12=1:1, Gibco) cell culturemedium containing 10% FBS, 1% PS, and 1.5 g/L Na₂CO₃ were used and thedensity of seeding cell concentrate was 150×10⁴ cells/μL. With additionsof 5 μL culture medium after 5 minutes, 100 μL culture medium after 10minutes, and 200 μL culture medium after 30 minutes followed bycontinuous addition of 200 μL culture medium each hour, the total volumewas adjusted to 1 mL. Cells were then incubated for 24 hours underconditions of 37° C. and 5% CO₂.

The freeze dried scaffold after incubation with cells was freeze driedfor 12 hours, then 1.5 mL of decomposition solution were added at 60° C.and the reaction was allowed to take place for 24 hours. 0.5 mL of thesolution after decomposition were added to 5 mL of dye and thefluorescence intensity (Excitation wavelength=365 nm, Emissionwavelength=458 nm) was measured using fluorphotometer. The amount ofcells was calculated according to the standard curve, while the seedingrate was calculated according to Formula 3.Seeding rate (%)=(NE−N)×100  Formula 3NE is the number of cells after culturing for 24 hours, and N is 150×10⁴cells.

rADAS was used to test the seeding rate, and as shown in FIG. 15, theseeding rate of PCL100^(s), PCL40EB60^(s), PCL80LL20^(s), andPCL80DL20^(s) scaffold were all greater than 90%, whereas the minimumseeding rate of PLC scaffold is 63.9±8.4%. Besides, the seeding rate ofPCL80LL20^(s) and PCL80DL20^(s) are 127.4±23.7% and 118.1±25.8%,respectively, indicating that cells can be successfully seeded ontoscaffold, and can survive and proliferate without the requirement of wetcondition.

4-3 Adhesion of Blood Platelet

The freeze dried waterborne biodegradable polyurethane membrane andsurface modified membrane were cut into appropriate size and wereattached to aluminum plate (diameter=2.4) using double adhesive tape.Then the plate was immersed in Hepe-Tyrodes buffer solution for an hour.After the buffer solution was discharged, blood platelet concentrate wasadded to fully cover the aluminum plate and allowed to settle in 5% CO₂incubation camber for an hour. Blood platelets that did not adhere tothe aluminum plate were washed away by washing with Hepe-Tyrodes bufferfor three times, and then Hepes solution containing 2% (v/v)glutaraldehyde (Riedel-deHaen) were added. Blood platelets were fixedfor 30 minutes and Hepes-Tyrode/double-distilled water solutions withconcentration gradient were used to immerse the plate for 1 minute toeliminate the salt on the surface. Same concentration gradient wasapplied and replaced with ethanol, and the plate was freeze dried usingfreeze dryer (FDU-1200, Eyela, Japan). Finally, the activation conditionof the blood platelet adhered onto the surface of the plate was observedusing scanning electron microscope (SEM, S-4800, Hitachi).

The amount of blood platelet adhered onto the surface and theiractivation degree before and after modifying the surface by sulfonatedchitosan can be used as indications for blood compatibility. As shown inFIG. 16, considerable adhesion and activation of blood platelet can beobserved before the surface modification, and PLA^(f), in particular, issignificantly higher than the others. A tendency to decrease regardingblood platelet adhesion and activation can be observed after the surfacemodification, wherein PCL40EB60^(f)-ASC is not significantly differentfrom PLA^(f)-ASC; PCL100^(f)-ASC, PCL80LL20^(f)-ASC, andPCL80DL20^(f)-ASC are significantly lower than PLA^(f)-ASC.Particularly, PCL80LL20^(f)-ASC and PCL80DL20^(f)-ASC show negligibleblood platelet adhesion and activation, indicating that the modificationdoes not result in blood coagulation.

The amounts of blood platelet adhesion before surface modification arerated as follow: PLA^(f)>PCL40EB60^(f)>PCL100^(f)>PCL80LL20^(f)PCL80DL20^(f); the levels of blood platelet activation are rated asfollow: PCL40EB60^(f)>PLA^(f)>PCL100^(f)≈PCL80LL20^(f)≈PCL80DL20^(f).

The amounts of blood platelet adhesion after surface modification arerated as follow:PLA^(f)-ASC≈PCL40EB60^(f)-ASC>PCL100^(f)-ASC>PCL80DL20^(f)-ASC≈PCL80LL20^(f)-ASC.

The levels of blood platelet activation are rated as follow:PLA^(f)-ASC>PCL40EB60^(f)-ASC≈PCL100^(f)-ASC>PCL80DL20^(f)-ASC≈PCL80LL20^(f)-ASC.

Thus, according to the above embodiments, compositions of PCL40EB60,PCL80LL20, and PCL80DL20 are found to be capable of being made intowaterborne biodegradable polyurethane emulsion in Example 1. Example 1also further instructs the emulsion being made into biocompatible andbiodegradable polyurethane in the form of membrane. Example 2 disclosesthat the inflammatory response caused by the membrane is not significantand proofs that, via in vitro and in vivo degradation test, thebiocompatible and biodegradable polyurethane exhibit biocompatibilityand biodegradability. According to Example 3, by using electrospinning,freeze drying, and particle-leaching/freeze drying, scaffolds withdiameters of pores on the surface and the cross-section sit within therange of the diameter of vascular graft endothelialization can beprepared. Example 4 further proofs that the scaffold made in Example 3does not posses significant blood coagulation function. Moreover, cellssuch as endothelial cells and adipose-derived stem cells cansuccessfully implant onto the scaffold and proliferate, indicatingbiocompatibility, hence, being one ideal material for vascular graft.

In addition, the waterborne biodegradable polyurethane was also preparedin the form of structurally opened 3D scaffold with stacking regularmicropillar (as shown in FIG. 17). Micropores with diameter of 1.94±0.6μM were also found to be spreading along each nanopillar. Pores of thissize are beneficial for the maintenance of cell morphology, thus can beapplied to sophisticated cell scaffold.

To understand whether the abovementioned scaffold is suitable for theincubation of mesenchymal stem cell, polyurethane sophisticated scaffoldwere sterilized for a day using ultraviolet light. Then, mesenchymalstem cells were used to carrier out the cell seeding experiment.Adipose-derived stem cells were extracted from rat adipose tissue, inwhich 1×10⁶ cells were suspended in 20 mL of culture solution to form acell concentrate. The cell concentrate was then seeded onto polyurethanescaffold and incubated for 4 hours. Finally, 3 mL of culture solutionwere added and the incubation was allowed to proceed for another 20hours. DNA dye Hoechst 33258 was used to perform cell count. The resultsindicates that after 24 hours of incubation, the number of cells isbetween 8.59×10⁵ to 8.77×10⁵ and the seeding rate is 86.8±0.9%, showingthat the scaffold is suitable for the incubation of mesenchymal stemcells such as adipose-derived stem cells.

EXAMPLE 5 Microsphere Prepared by Using the Waterborne BiodegradablePolyurethane Emulsion

Spraying process can be applied to the preparation of waterbornebiodegradable polyurethane microsphere, for instance, directly spray thewaterborne biodegradable polyurethane into liquefied nitrogen thenundergo freeze drying. This process can also be incorporated bythermal-induced phase separation (TIPS) and wet-phase separation. Themicrosphere prepared has diameter of 20 to 60 μm with microporousstructure.

To test the ability of microsphere as a drug carrier, firstly, methyleneblue was mixed with waterborne biodegradable polyurethane PCL40EB60 andPCL 100. Then, microspheres having diameter of 20 μM were formedaccording to the above method. The microspheres having methylene bluewere immersed in phosphate buffered saline (PBS) at 37° C. for 2, 4, 8,12, 24, 48, and 72, hours, respectively. Then UV/vis spectrometer wasused to measure the absorption at 660 nm for quantification. As shown inFIG. 18, the result of drug release of the microsphere, the amount ofdrug released of PCL40EB60 microsphere is much higher than the amount ofdrug released of PCL100 microsphere, however, both PCL40EB60 microsphereand PCL100 microsphere have drug carrying capabilities.

In addition, the cell carrying capability of the microsphere was tested.L929 cell was loaded at a density of 1×10⁵ cells/well. PCL100microsphere was added (0.1 g/well) or TCPS was applied. The cells werethen incubated under conditions of 37° C. and 5% CO₂ for 24 hours and 72hours followed by observation of the number of cells. As shown in theresult of FIG. 19, the number of cells incubated with PCL100 microsphereis significantly higher than the number of cells incubated by TCPS,indicating that PCL100 microsphere has cell carrying capability.

What is claimed is:
 1. A waterborne biocompatible and biodegradableelastomer, comprising: a main chain of polyurethane comprising a hardsegment and a soft segment, the hard segment is formed by reaction ofdiisocyanate, 2,2-bis(hydroxymethyl)propionic acid and a chain extender,and the soft segment is a biodegradable oligomer diol, wherein thebiodegradable oligomer diol is made of a polycaprolactone diol and adiol selected from the group consisting of polyethylene butylene adipatediol, polylactic acid diol, and any combinations thereof; and whereinthe molar ratio of diisocyanate: soft segment:2,2-bis(hydroxymethyl)propionic acid: chain extender of the product is3-4:1:1-2:1.52.
 2. The waterborne biocompatible and biodegradableelastomer of claim 1, wherein the polylactic acid diol is L-lactic acidor DL-lactic acid.
 3. The waterborne biocompatible and biodegradableelastomer of claim 1, wherein when the soft segment is consisted ofpolycaprolactone diol and polyethylene butylene adipate diol, thepolycaprolactone diol is in an amount of greater than 0.3 molar fractionof the degradable oligomer diol.
 4. The waterborne biocompatible andbiodegradable elastomer of claim 1, wherein when the soft segment isconsisted of polycaprolactone diol and polylactic acid diol, thepolycaprolactone diol is in an amount of greater than 0.4 molar fractionof the degradable oligomer diol.
 5. The waterborne biocompatible andbiodegradable elastomer of claim 1, wherein when the soft segment isconsisted of polycaprolactone diol and polylactic acid diol, thepolycaprolactone diol is in an amount of greater than 0.8 molar fractionof the degradable oligomer diol.
 6. The waterborne biocompatible andbiodegradable elastomer of claim 1, wherein the diisocyanate isalicyclic polyisocyanate.
 7. The waterborne biocompatible andbiodegradable elastomer of claim 6, wherein the alicyclic polyisocyanateis isophorone diisocyanate.
 8. The waterborne biocompatible andbiodegradable elastomer of claim 1, wherein the chain extender isethylenediamine.
 9. The waterborne biocompatible and biodegradableelastomer of claim 1, wherein the amount of the soft segment is between45% and 75% w/w of the total weight of the elastomer.
 10. A waterbornebiocompatible and biodegradable elastic membrane made of thebiocompatible and biodegradable elastomer of claim 1, wherein theYoung's modulus of the biodegradable elastic membrane is greater than0.5 MPa and smaller than 40 MPa.
 11. The waterborne biocompatible andbiodegradable elastic membrane of claim 10, wherein the tensile strengthof the biodegradable elastic membrane is greater than 5 MPa.
 12. Thewaterborne biocompatible and biodegradable elastic membrane of claim 1,wherein the elongation of the biodegradable elastic membrane is greaterthan 400%.
 13. A vascular graft made of the waterborne biocompatible andbiodegradable elastomer of claim 1, wherein a plurality of pores arepresent on the wall of the vascular graft with an average pore diameteron the outer surface is between 5 to 50 μm, and an average pore diameteron the cross-section is between 10 to 100 μm.
 14. The vascular graft ofclaim 13, the elongation of the vascular graft is greater than 220%. 15.The vascular graft of claim 13, wherein the pores are made by usingfreeze drying.
 16. The vascular graft of claim 13, wherein the pores aremade by using particle-leaching method.
 17. The vascular graft of claim13, wherein the surface of the wall of the vascular graft is chemicallymodified.
 18. A carrier made of the waterborne biocompatible andbiodegradable elastomer of claim 1, wherein the carrier is present inthe form of microsphoere, hydrogel, nanodispersion,nanodispersion-coated inorganic nanoparticle, foam, electrospinningfiber, or scaffold.
 19. The carrier of claim 18, wherein the carrier isused for carrying a cell, a gene, or a drug.
 20. The carrier of claim18, wherein the carrier exhibits electronegativity, amphiphilicity, andanticoagulant ability.
 21. The waterborne biocompatible andbiodegradable elastomer of claim 1, wherein the molar ratio ofdiisocyanate: soft segment: 2,2-bis(hydroxymethyl)propionic acid: chainextender of the product is 3.52:1:1:1.52.